A $US5000 reward has been put up for information on how a rare white wolf at Yellowstone National Park was shot dead.
The female was one of three white wolves in the park and had 14 living pups, wildlife officials say.
The reward comes after initial results of a necropsy show the so-called White Lady was shot around 10 April.
"She was one of the most recognisable wolves and sought after by visitors to view and photograph," the park said.
"Due to the serious nature of this incident, a reward of up to $5,000 is offered for information leading to the arrest and conviction of the individual(s) responsible for this criminal act," said Yellowstone National Park Superintendent Dan Wenk.
At 12 years old, she had lived for more than twice the average lifespan of a wolf in Yellowstone, officials say.
The Canyon Pack Alpha, as she was known to wildlife researchers (and as The White Lady to tourists), was found by hikers on 11 April.
Wildlife officials were not able to save its life, and the wolf was put down.
Her remains were brought to a US Fish & Wildlife Service Forensics Laboratory in Oregon for a necropsy, where officials determined that it had been mortally wounded by a hunter's rifle.
As of 2014, researchers had documented at least 104 wolves in 11 packs located within the park.
The wolves were reintroduced in Yellowstone in 1995, having been eradicated by hunters.
Advocates of wolves say the presence of predators helps balance the ecosystem, and leads to healthier populations of other wild animals.
Opponents say they are a threat to humans, pets and livestock.